This invention relates to a circuit which is integrated on a semiconductor substrate for level conversion or for driving a load, (for example, Vacuum Fluorescence Displays, with a comparatively high voltage (for example, 35 V), comprising a first and a second supply voltage terminal for application of the comparatively high voltage, an input and an output, a switching transistor, a protection transistor and a sub-circuit, the switching transistor and the protection transistor being connected in series, the gate of the switching transistor being connected to the input, the source of the switching transistor being connected to a first supply voltage terminal, and the drain of the protection transistor supplying a signal for the sub-circuit during operation, an output of the sub-circuit being connected to the output and the gate of the protection transistor receiving a fixed voltage.
A circuit of this kind is known from Proceedings of the IEEE Custom Integrated Circuits Conference, Portland, Oregon, May 4-7, 1987, pp. 267-271. In circuits of this kind it is important to ensure that no breakdowns occur in any location due to excessive field strengths, especially at the drain or gate junctions. A comparatively high voltage is a voltage at which the drain junction of the switching transistor would break down.